1. Field of the Invention
The present invention relates to a method and apparatus for controlling the operation of a pellet mill which is used to compress raw ingredients into extended pellets livestock feed and the like. More specifically, the present invention relates to a controller for optimizing the operation of a pellet mill for a variety of ingredients and pellet sizes.
2. Background Art
The forming of dry, finely milled materials (typically referred to as "mash") into larger pellets permits the materials to be more efficiently handled, minimizing dust and loss. When there are multiple ingredients, pelletizing insures the ingredients are delivered in a consistent ratio without separation or settling. In the livestock industry, where pellets are formed of ground feed materials, pelletizing can reduce the waste of costly additives such as vitamins, hormones and antibiotics and prevent selective feeding by the livestock guaranteeing that they receive the intended formulation.
The forming or "pelleting" of dry ingredients into pellets is accomplished by a pellet mill. Typically, a pellet mill consists of a die in the form of a large hollow cylinder having a number of radially extending holes through which pellets may be extruded. The inner surface of the cylinder contacts the rolling faces of a plurality of rollers which squeeze the ingredients to be pelletized through the die when the die is rotated about the rollers. The extruded pellets, initially long, solid cylinders, are broken across their length into smaller pieces.
In order to improve the cohesion of the dry ingredients and to improve their nutritional quality, the ingredients are processed, prior to introduction to the pellet mill die, in a conditioner which mixes the ingredients together, introduces liquids and heats the ingredients to a desired temperature.
As with most industrial equipment, it is desirable that the pellet mill be operated at high efficiency. This requires that the down time of the pellet mill be minimized, and that the throughput of the pellet mill, while running, be maximized. One cause of down time is the plugging of the die by the ingredients. Such plugging may require that the pellet mill be stopped and the dies removed so that the plugged orifices may be opened. Once this is accomplished, further time may be wasted restarting the mill as the conditioner is refilled and the new ingredients heated and moistened. Because the mechanisms of plugging are not well understood and may differ for different ingredients, it is typical that the pellet mill is operated at a conservative rate significantly below its potential throughput.